1. Field of the Invention
The present invention relates to a semiconductor device and method of manufacturing the semiconductor device, and more articularly, to a GaInNAs-based semiconductor device and a method of manufacturing the GaInNAs-based semiconductor device.
2. Description of the Background Art
A quantum leap has recently been made in the volume of information transmitted over the Internet, and an improvement in transmission speed is an urgent challenge to be met. Trunk optical fiber communication has currently achieved a transmission speed of Class 10 Gbit/s. However, the transmission speeds of subscriber systems have become a bottleneck, and the real state is that browsing a home page is time-consuming. At the dawn of an era of full-fledged broadband communication, a further improvement in the transmission speeds of the subscriber systems, the so-called xe2x80x9clast-one-mile,xe2x80x9d has been zoomed in on as an indispensable requirement.
Two potent measures are available for improving the transmission speeds of subscriber systems; that is, (1) upgrading of an optical fiber network for subscribers, and (2) building of point-to-multipoint communication utilizing a millimeter wave/quasi-millimeter wave. A semiconductor laser producing light having a wavelength of about 1.3 xcexcm is a key device for optical fiber communication, and a monolithic microwave integrated circuit (MMIC) for transmission/receiving purposes is a key device for millimeter-wave/quasi-millimeter-wave communication. Accordingly, an improvement in the performance of the semiconductor devices (i.e., the semiconductor laser and MMIC) and a great reduction in the costs of the semiconductor devices are indispensable for proliferating the optical fiber network for subscribers and point-to-multipoint communication.
An InGaAsP laser formed on an InP substrate or an InGaAs/AlGaAs strained quantum well laser formed on a GaAs substrate has recently been utilized as a light source for optical fiber communication.
The InGaAsP laser has a problem of an operating current increasing abruptly with an increase in temperature; that is, a problem of a so-called vicious temperature characteristic. The reason for this is that the InGaAsP-based semiconductor layer fails to ensure a large amount of band discontinuity existing between a well layer and a barrier layer, and is that the bandgap of the semiconductor laser has great temperature dependence. Accordingly, use of the InGaAsP laser involves a necessity for use of an additional temperature controller, thus rendering the communications system expensive. As mentioned previously, realization of a subscriber optical communication system requires development of a low-price system which does not involve use of a temperature controller.
In contrast with the InGaAsP laser, the InGaAs/AlGaAs strained quantum well laser ensures the existence of a large amount of band discontinuity between the well layer and the barrier layer, and hence the bandgap of the quantum well laser has low temperature dependence. Accordingly, the quantum well laser has a superior temperature characteristic, thus obviating the need for a temperature controller. An increase in a composition ratio of In results in a problem of an increase in the difference between a lattice constant of InGaAs and that of AlGaAs. Hence, there cannot be obtained a high-quality crystal, and a laser producing light having a wavelength of about 1.3 xcexcm used in optical communication has not been formed thus far.
To solve the problem, attention has recently been focused on a new compound crystal semiconductor called GaInNAs. A bandgap corresponding to 1.3 xcexcm to 1.5 xcexcm is realized by means of adding a trace amount (1% through 5%) of nitrogen (N) to InGaAs. Use of InGaAs for a well layer and use of GaNAs or GaAs for an optical confinement or barrier layer enables a sufficient amount of band discontinuity. A semiconductor laser which obviates a need for temperature control can be realized. A large-diameter, low-cost GaAs substrate can be used in lieu of an expensive InP substrate. Hence, in addition to obviating a necessity of a temperature controller, use of the low-cost GaAs substrate brings an expectation for a significant decrease in the cost of a communication system.
However, GaInNAs is susceptible to three-dimensional island-shaped growth, thus posing a difficulty in fabricating a quantum well structure having a flat interface. For this reason, there has been available only a report about a laser having a high oscillation threshold value (threshold-value current), and the problem poses a barrier against practical use of GaInNa.
The present invention has been conceived to solve the previously-mentioned problems and aims at causing a good-quality GaInNAs crystal to grow on a GaAs substrate.
The present invention also aims at providing a semiconductor laser for optical communication which obviates a need for temperature control in a less expensive manner by use of GaInNAs, as well as providing a transistor of high trans conductance or a high-power high-frequency integrated circuit.
The above objects of the present invention are attained by a following method of forming a GaInNAs layer.
According to one aspect of the present invention, in the method of forming a GaInNAs layer on a substrate, thallium is caused to adhere to the substrate. GaInNAs crystal is caused to grow on the substrate after adhesion of thallium.
According to another aspect of the present invention, in the method of forming a GaInNAs layer on a substrate, GaInNAs crystal is caused to grow on the substrate by means of simultaneously supplying material gas to be used for forming the GaInNAs layer and thallium.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.